A rotary stone-cutting head normally has a body generally centered on and adapted to be rotated in a predetermined direction about a normally upright axis. One axial face, normally the bottom one, of this body has a plurality of teeth having cutting edges that are directed angularly generally forwardly in a predetermined direction of rotation of the body about its axis. A suction arrangement opens at the normally open center of the body so that chips and so on freed by the teeth are carried off, normally along with water or another liquid fed to the tool to lubricate and cool it as well as to serve as a vehicle for the freed chips.
These cutting edges therefore do virtually all of the removal work. Hence they get quite hot and are subjected to enormous wear. Thus it is standard practice to form these teeth of separate hardened-steel elements that are secured to the face of the drilling or cutting head. To this end appropriately edged small hardened-steel plates are brazed or soldered to appropriate seats on the front or lower body face.
German utility model No. 7,828,385, German patent publication No. 2,841,523, and U.S. Pat. No. 2,984,028 describe such an arrangement wherein the teeth supports are radially outwardly projecting and tapered pins. The teeth have tapered recesses that fit snugly over these pins, and a wedge or the like passing through appropriate transverse holes in the teeth and supports hold these teeth in place on the respective supports.
In such an arrangement the teeth are not subject to even wear. The large head inherently rotates relatively slowly, so that a hard node in the rock can be uncovered by one tooth and then engaged solidly by the next one. Similarly as the head moves into contact with the rock, which inherently has some voids and soft spots, it subjects some of the teeth to much greater wear than others. Thus it is fairly common for the hardened edge of a tooth to be broken by suddenly engaging a hard spot, as such hardened edge has less give than the softer cast iron of the teeth.
In my copending patent application No. 389,970 filed 18 June 1982 I describe a rotary stone-cutting head of the standard type, that is having a body generally centered on and adapted to be rotated in a predetermined direction about an axis. According to this earlier invention an array of cutter supports on the body directed at least partially in the direction carry respective cutter teeth each having relative to the axis an outer cutting edge and relative to the direction a generally angularly forwardly directed face adjacent the edge and formed with an array of holding recesses. The teeth are at least at the edges of hardened metal. Means removably secures the teeth to the respective supports and respective hardened-metal breaking pins have shanks fitted to the recesses and points directed angularly forwardly in the direction. At least some of the points lie angularly ahead in the direction of the respective cutting edge.
These points have a crushing effect that greatly augments the effectiveness of the cutter head. Preliminarily engaging the stone surfaces with these crushing or breaking points makes for much more efficient overall material removal in conjunction with subsequent cutting or peeling of the surface. In addition these pins strike hard nodes and the like before the cutting edges to reduce wear on these parts.
Such an arrangement has shown to give superior results. Nonetheless the hardened-metal parts of the teeth do get broken rather frequently. The teeth are quite expensive to manufacture, as each must be bored out for a group of the breaking pins.